The failure of synthetic polymeric medical devices - Durability and Reliability of Medical Polymers - page 207

such as intraocular lenses (iOLs), silicone is an excellent choice for the
replacement lens (Fig. 9.26). They replaced the original PMMA lenses
developed in the UK for RAF pilots who had been injured during the Battle
of Britain. Unreinforced silicone lenses are optically clear and replace a
diseased lens, where cataracts have reduced if not eliminated vision in
the eye affected. 16 The silicone lens is rolled up and injected through a
small slit in the outer eye covering; it then unrolls and fills the cavity. The
device is only lightly stressed throughout injection, and almost unstressed
when in the eye, so the chance of mechanical failure is very low. However,
problems can arise in delivering the lens to the eye via the polypropylene
injector in its rolled-up state (Fig. 9.27 and 9.28). Low friction in the tube
is critical and this is achieved by adding calcium stearate to the polymer

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9.26 Design of flexible intraocular lens (US patent 4,717,906; 1988).

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9.27 Plastic injectors for inserting the IOL into the eye.